This invention relates to a marine propulsion system, an more particularly to an improved coolant pump for circulating coolant through the cooling system of a marine propulsion system.
The invention is directed to a marine propulsion system in which coolant water is taken in through intake ports in the submerged lower unit of the system and thereafter circulated through the engine cooling system. In a typical arrangement for circulating cooling water through the cooling system, a water pump includes an impeller interconnected with a drive shaft which is rotatable in response to rotation of the engine crankshaft. In this manner, the impeller acts to circulate water through the cooling system whenever the engine is running. In such an arrangement, the portion of the drive shaft which is coupled to the pump impeller is exposed to intake cooling water. In fresh water applications, this generally does not present a problem. However, when the intake cooling water is from a salt water body, such exposure of the engine drive shaft to salt water can cause corrosion problems in the drive shaft, which is typically constructed from a carbon steel material. If the portion of the drive shaft to which the pump impeller is connected corrodes excessively, then it may be necessary to replace the entire drive shaft.
One solution to the above-noted problem is to construct the drive shaft of a corrosion resistant material, such as stainless steel. However, corrosion resistant materials such as stainless steels are generally quite expensive, resulting in a high cost solution to a problem which only affects a portion of the drive shaft.
The present invention is designed to allow use of a standard carbon steel drive shaft in a salt water application, while isolating that portion of the carbon steel drive shaft which drives the water pump impeller from the intake cooling water circulating through the engine cooling system. In accordance with the invention, a corrosion resistant coolant pump for placement in the cooling system of a marine drive includes a housing having a cavity in communication with the marine drive cooling system. A corrosion resistant member is mounted to and rotatable with a drive shaft, which is interconnected with the engine crankshaft so as to be rotatable in response to rotation thereof. An impeller disposed within the housing cavity and is connected to the corrosion resistant member. The impeller is rotatable in response to rotation of the corrosion resistant member caused by rotation of the drive shaft, for pumping coolant through the cooling system. Seal means is provided about the corrosion resistant member for sealing the housing cavity and preventing contact of coolant with the rotatable shaft. In one embodiment, the corrosion resistant member comprises a cup formed from a corrosion resistant material, such as stainless steel. The cup includes an inner passage adapted to receive and enclose an end of the rotatable drive shaft. The cup is interconnected with the engine drive shaft so as to be rotatable therewith, such as by a key and groove connection or the like. The cup preferably includes a portion extending into the housing cavity, and the impeller is preferably connected to the portion of the cup extending into the housing cavity. The seals means preferably comprises a pair of seals for isolating the carbon steel drive shaft from the coolant circulating within the housing cavity. In one embodiment, a first seal is provided adjacent the housing cavity, and a second seal is spaced from the first seal so as to form a gap there-between. A drain means is in communication with the gap formed between the first and second seals for draining any coolant which may leak past the first seal prior to its contacting the drive shaft by leaking through the second seal.
The invention thus provides a relatively inexpensive solution to the problem of drive shaft corrosion when operating the marine drive in a salt water environment. A standard carbon steel drive shaft is employed and only a relatively small part, namely the cup mounted to the end of the drive shaft, is constructed of the expensive stainless steel material.